The present invention relates to a multi-layered metal line of a semiconductor device and a method for forming the same, and more particularly to a multi-layered metal line of a semiconductor device, which has an excellent diffusion barrier and a method for forming the same.
Memory cells in a highly integrated semiconductor device are formed in a stacked structure in order to meet the high operational speed requirements. Further, a metal line for carrying the electric signals to the memory cells are formed in a multi-layered structure. The multi-layered metal lines provides advantageous design flexibility and allows more leeway in setting the margins for the wiring resistance, the current capacity, etc.
Aluminum has been the choice material for a metal line for its superior electric conductivity and the ease of being applied in a fabrication process. However, it is not the case when the design rule is so decreased for higher integration of a semiconductor device, because the resistance of the metal line made of aluminum increases to a undesirable level. To cope with this problem, copper is used as the material for a metal line instead of aluminum as the resistance of copper is relatively lower.
In a process for forming a metal line using copper, the copper, unlike aluminum, diffuses through an interlayer dielectric. The copper diffused to a semiconductor substrate acts as deep-level impurities in the semiconductor substrate and induces a leakage current. Therefore, in the case of a metal line formed using copper, a diffusion barrier must be necessarily formed not only where the copper comes into contact with hetero-metal but also on a portion of an interlayer dielectric on which the copper is formed in order to decrease the leakage current due to diffusion of copper.
In general, as a diffusion barrier for a metal line formed using copper, a Ti/TiN layer or a Ta/TaN layer is mainly used.
Nevertheless, the Ti/TiN layer or Ta/TaN layer, which is used as a diffusion barrier in the metal line formed using copper, is significantly decreased in suppressing the diffusion of copper in an ultra-highly integrated device below 40 nm and cannot properly perform its function as a copper diffusion barrier.